Multiple interleaved phased antenna array providing simultaneous operation at two frequencies and two polarizations

ABSTRACT

A phased array antenna including within its single electromagnetic radiating aperture two or more groups of radiating elements, each group of radiating elements being distinguished by the polarization and frequency spectrum of its radiation. The radiating elements of each group are of sufficiently small physical size compared to their free space wavelength to permit their being interleaved among the radiating elements of the other groups in a configuration whereby each group of radiating elements has approximately the same control of the beamwidth and the steering of its beam of radiation as would be the case if only one of these groups were present.

Sttes ate t atelier et al.

MULTIPLE INTERLEAVED PHASE!) ANTENNA ARRAY PROVIDING SIMULTANEOUSOPERATION AT TWO FREQUENCIES AND TWO POLARIZATIONS lnventors: Burrell R.Hatcher, Bedford; Aldo R. Miccloli, Acton; Max C. Mohr,

Chelmsford; Edward J. Sheldon, Lexington, all of Mass.

Assignee: Raytheon Company, Lexington,

Mass.

Filed: Feb. 3, 1971 Appl. No.: 112,395

Related lJ.S. Application Data Continuation of Ser. No. 779,767, Nov.29, 1968, abandoned.

US. Cl ..343/754, 333/31 R, 343/778, 343/854 Int. Cl. ..l'l0lq 19/08Field of Search ..343/725, 754, 771, 776-779, 343/853, 854

3,259,902 7/1966 Malech ..343/777 X 3,480,958 11/1969 Tcheditch..343/854 X 3,243,818 3/1966 l'loltzman ..343/77l 3,267,477 8/1966Brickey ..343/779 X 3,281,851 10/1966 Goebels, Jr.... ....343/77l X3,482,248 12/1969 Jones, Jr ....343/771 X 3,500,422 3/1970 Cheston et a1..343/778 3,518,695 6/1970 Schroeder .343/854 3,553,706 1/1971 Charlton..343/853 Primary Examiner-Paul L. Gensler Attorney-Harold A. Murphy,Joseph D. Pannone and Herbert W. Arnold [57] ABSTRACT A phased arrayantenna including within its single electromagnetic radiating aperturetwo or more groups of radiating elements, each group of radiatingelements being distinguished by the polarization and frequency spectrumof its radiation. The radiating elements of each group are ofsufficiently small physical size compared to their free space wavelengthto permit their being interleaved among the radiating elements of theother groups in a configuration whereby each group of radiating elementshas approximately the same control of the beamwidth and the steering ofits beam of radiation as would be the case if only one of these groupswere present.

19 Claims, 7 Drawing Figures PMENMBHEB 1 I 72 3. 706, 998

sum 1 BF 3 INVENTORS BURRELL R. HATCHER ALDO R. M/GG/OL/ MAX 6. MOHREDWARD J SHELDON Y 71 W /M ATTORNEY PATENTED E R 9 @972 3,706,998

SHEET 2 BF 3 I/VVENTORS BURRELL RHATGHER ALDO R. M/GC/OL/ MAX 6 MOHREDWARD J. SHELDON ATTORNEY PATENFEE m 19 m2 SHEET 3 BF 3 //V VE IV 7'0/?8 HA TCHER BURRELL R ALDO R. M/CC/OL/ MAX 0. MOHR EDWARD .1. SHELDONBy /c [a I ZK fl ATTORNEY MULTIPLE INTERLEAVED PHASED ANTENNA ARRAYPROVIDING SIMULTANEOUS OPERATION AT TWO FREQUENCIES AND TWOPOLARIZATIONS This application is a continuation of application Ser. No.779,767, filed on Nov. 29, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to antennas having aplurality of electromagnetic radiating elements, and more particularly,to the utilization ofa single radiating aperture having elements ofdiffering characteristics to provide a capability to operatesimultaneously at more than one frequency band, polarization state andscan sector or any combination of these three.

An installation employing two or more phased array antennas is requiredfor certain applications as in the situation where signals of differingcarrier frequencies or polarizations are required to be transmitted to asingle target vehicle. Such installations typically require a number ofsupport structures for the individual phased array antennas which entailconsiderable weight, space, and auxiliary equipment.

It is therefore desirable to provide an antenna having a singleelectromagnetic radiating aperture which combines the features of aplurality of individual antenna arrays. These features include, forexample, a frequency diversity capability and a capability to transmitin the various frequency bands and in the polarizations of theindividual arrays as well as means for steering each of the plurality ofbeams of radiation. This aperture need be no larger than the aperturesof the largest individual antenna since each beam of radiation isgenerated independently of the other beams and therefore the aperturedimensions of the individual array are adequate to form the beam. Asingle aperture antenna of this sort is particularly advantageous formobile applications, for example, where a phased array radar is to bemounted on a space vehicle or aircraft. In addition to the savings inspace, weight, and expense, this antenna also provides a common axis forthe plurality of beams of radiation.

In order for an antenna having a single aperture to generatesimultaneously the beams of electromagnetic radiation which arecharacteristic of each of a plurality of individual antenna arrays andmore particularly, of a plurality of individual phased array antennas inwhich the phases of radiation of the individual radiating elements arevaried with respect to one another to provide beam steering or scanning,it is frequently required to have the means to simultaneously transmitat different frequencies and polarizations and to generate a pluralityof beams of radiation such that each beam is steered independently ofthe other beams. These requirements are met by the use of a plurality ofradiating elements which have the characteristics of the radiatingelements of the individual array. However, an important problem arisesrelating to physically locating these elements within a single aperture,since within a conventional array having a single type of radiatingelement all such radiating elements are typically contiguous withoutspaces between them large enough to accommodate similar radiatingelements. Also, the interelement spacing, that is, the distance betweencenters of the radiating elements of an individual array cannot beincreased to provide spaces for other radiating elements, because theinterelement spacing plays a critical role in forming the beam ofradiation. For example, an increase in the interelement spacing altersthe beamwidth and such increase can be great enough to produce gratingnulls in the antenna directivity pattern, particularly at large scanningangles. It is, therefore, desirable to provide an improved antenna arraycomprising electromagnetic radiating elements with radiationcharacteristics similar to those of two or more individual arrays, andhaving an antenna radiating aperture whose physical size is no largerthan the radiating aperture of the largest of the individual arrays.

It is an object of the present invention to provide a novel antennaarray which generates beams of radiation having approximately the samebeamwidths, polarization, and frequency spectrums as the beams ofradiation generated by a plurality of individual arrays, yet has aphysical structure which weighs less, and is more economical toconstruct than the total of the plurality of structures of theindividual arrays.

It is also an object of the present invention to provide an improvedphased array antenna which transmits simultaneously at two frequenciesand generates two beams of radiation one at each frequency such that thetwo beams can be coaxial.

SUMMARY OF THE INVENTION In accordance with the invention, an antennaarray is constructed of electromagnetic radiating elements drawn fromtwo or more individual arrays of radiating elements wherein each of saidindividual arrays is identified by the characteristics of directivitypattern, polarization, and frequency spectrum of the beam of radiationswhich it generates. A group of electromagnetic radiating elements drawnfrom each of said individual arrays are dielectrically loaded to be ofsufficiently small physical size compared to their free spacewavelengths to permit their being interleaved among the radiatingelements drawn from each of the other individual arrays, and theconfiguration and spacing of the interleaved radiating elements is suchthat the above characteristics of the individual arrays are retained. Inthe interleaved antenna array, the interelement spacing, namely, thespacing between centers of the radiating elements drawn from any onegroup, is typically approximately one-half the free space wavelength ofthe radiation generated by these elements. Accordingly, each radiatingelement of each of said groups is constructed with a physical size whichis smaller than the interelement spacing to permit the radiatingelements to be spaced in said array with the aforementioned one-halffree space wavelength spacing between centers.

In the case of an antenna array which is formed by interleaving twogroups of electromagnetic radiating elements, it is preferable that thepolarization of the radiation which is characteristic to the radiatingelements of one group be orthogonal to the polarization of the radiationwhich is characteristic to the radiating elements of the second group inorder to minimize a cross coupling between the two groups of radiatingelements. With this arrangement, a beam of radiation generated by theradiating elements of one group as, for example, with a phased arrayantenna, can be scanned continulOGOll 0137 ously through a sector ofspace approximately independently of the beam of radiation generated bythe radiating elements of the second group.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned objects and otherfeatures of the invention are explained in the following descriptiontaken in connection with the accompanying drawings wherein:

FIG. 1 is an isometric view of one embodiment of this invention having areflector-type optically fed antenna array, the antenna array havingelectromagnetic radiat' ing elements of two different frequencies, saidelements being interleaved so that the spacing between centers of thelower frequency radiating elements is equal to twice the spacing betweencenters of the higher frequency radiating elements;

FIG. 2 is an enlarged fragmentary isometric view of the antenna arraytaken along the line 2-2 of FIG. 1;

FIG. 3 is an isometric view, partially cutaway, of one embodiment of aradiating element of the array of FIG. 1 wherein the radiating aperturehas a diameter which is approximately 0.2 wavelengths of the radiationtransmitted by this radiating element;

FIG. 4 is a fragmentary perspective view of a portion of an alternativeembodiment of the interleaved array of FIG. 1 wherein the spacingbetween centers of the lower frequency radiating elements is equal tothe spacing between centers of the higher frequency radiating elements;

FIG. 5 is an enlarged fragmentary perspective view of a portion of analternative embodiment of the interleaved antenna array of FIG. 1wherein the spacing between centers of the lower frequency radiatingelements is greater by a factor of 3 than the spacing between centers ofthe higher frequency radiating elements;

FIG. 6 is an enlarged fragmentary perspective view of a portion of analternative embodiment of the interleaved antenna array of FIG. 1wherein the spacing between centers of the lower frequency radiatingelements is equal to twice the spacing between centers of the higherfrequency radiating elements, and wherein a lower frequency radiatingelement is mounted beneath and coaxial with a higher frequency radiatingelement; and

FIG. 7 is a fragmentary view, partially in section, ofa higher frequencycoaxially mounted radiating element and its mounting strut.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I, there is shown aphased array antenna 10 which includes an interleaved antenna array 12which serves as a reflecting surface for directing electromagneticradiation to the feed horns l4 and 16 for receiving said radiation, andduring transmission, for collimating the radiation from the feed horns14 and 16 to form individual beams of radiation. The phased arrayantenna 10 is adapted to operate in a novel manner simultaneously withradiation at two frequencies and two polarizations. The higher frequencyradiation has a circular polarization of one sense, that is, clockwiseor counterclockwise and is reflected from the smaller radiating elements18, two of these elements being designated 18A and 18B. The lowerfrequency radiation has a circular polarization of the opposite sense inorder to minimize cross-coupling between the higher and lower frequencyradiating elements and is reflected from the larger radiating elements20, one of which is designated 20A. In transmitting electromagneticradiation, the antenna 10 operates in the manner of phased arrayantennas where each group of radiating elements 18 and 20 imparts aphase shift to radiation emanating from the high frequency born 14 andthe low frequency horn 16 to direct it in the desired direction. Inreceiving electromagnetic energy, the radiating elements 18 and 20direct the received radiation which is incident upon the face of array12 in the directions respectively of the feed horns 14 and 16. Theamount of the phase shift is controlled by computer-generated signals,not shown, applied to each of the, radiating elements. The feed horns 14and 16, as shown, are of different physical dimensions to accommodatethe two frequencies, the horn 14 having a smaller cross section tooperate at the higher frequency and the born 16 having a larger crosssection to operate at the lower frequency. Electromagnetic energy fromeach horn illuminates the entire face of the array.

The antenna 10 is provided with a support structure comprising ametallic mounting plate 22 and supporting struts 24. The metallicmounting plate 22 also serves as a ground plane for the radiation, andcan be hexagonal, as shown, or of any convenient form, such as circularor square, and is provided with apertures to receive the radiatingelements 18 and 20, and hold these elements 18 and 20 spaced in a mannerto be described. The struts 24 support the mounting plate 22 and alsosupport transmitting and receiving equipment contained in metalliccabinet 26. The feed horns 14 and 16 are connected to the transmittingand receiving equipment and extend outwardly from the electronicscabinet 26. The feed horns are rigidly attached to the mounting plate 22by means of a bracket 28. As shown in FIG. I, the higher and lowerfrequency radiating elements 18 and 20 are uniformly distributedthroughout the interleaved array 12 so that the high and low frequencybeams of radiation generated by the antenna 10 are coaxial.

The arrangement and means for mounting the radiating elements 18 and 20are shown in FIG. I and in greater detail in the enlarged fragmentaryview of FIG. 2. The radiating elements 18 and 20 are arranged in aconfiguration, as' seen in FIG. 2, in which each of the larger size,lower frequency elements 20 abuts three smaller-size, higher frequencyelements 18 located in equally spaced-apart relation around theperiphery of said larger element 20. Thereby lines, now shown,connecting the three elements form an equilateral triangle or cell. Thesmaller size, higher frequency elements 13 are located with respect toeach other at the intersections of three sets of parallel lines, notshown, which form a grid having cells, each of which is in the form andsize of said equilateral triangle. The spacing between the centers ofthe higher frequency radiating elements 18 is approximately one-halfwavelength of the radiation which is transmitted by the radiatingelement 18. The higher frequency is, by way of example, equal to twicethe lower frequency and therefore the lower frequency radiating elements20 are shown with I060l l 0138 a diameter that is twice as large as thediameter of the higher frequency elements 18. The lower frequencyelements are similarly positioned at the intersections of three sets ofparallel lines, not shown, which form another grid having equilateraltriangular cells whose sides are twice as long as those of theaforementioned grid for the higher frequency elements 18, so that thespacing between centers of the lower frequency elements 20 is twice aslarge as the spacing between centers of the higher frequency elements18. It is convenient to define a spacing ratio which is the ratio of thespacing between centers of the larger size, lower frequency elements 20to the spacing between centers of the smaller size, higher frequencyelements 18. In the embodiment of FIG. 1 and FIG. 2 the spacing ratio is2:1, so that the high and low frequency beams of radiation can besteered over approximately the same range of beam steering angles thatdo not introduce grating nulls.

The radiating elements 18 and 20 are affixed with their axesperpendicular to the mounting plate 22 by mounting bolts 30, one ofwhich is designated 30A. The bolts 30 are tightened against the lips 32of recessed portions 34 of a higher frequency radiating elementsmounting flange 36 and are similarly tightened against the lips 38 ofrecessed portions 40 of a lower frequency radiating elements mountingflange 42. The lips 32 and 38 and the recessed portions 34 and 40 havedimensions which permit a single mounting bolt, such as bolt 30A, to beutilized at the point of proximity between two abutting radiatingelements such as the elements 18A and 20A. In the configuration of FIG.1 and FIG. 2, there are also higher frequency elements which do not abuta low frequency element, such as the higher frequency element 18B. Eachof the higher frequency elements 18 are spaced in the aforementionedconfiguration to be equidistant from each neighboring high frequencyelement. In FIG. 2, there is also shown a cartridge or case 44 andmatching structure 46 for each higher frequency element, and a cartridgeor case 48 and matching structure 50 for each lower frequency elementwhich are described below.

Referring to FIG. 3, there is shown a detailed isometric view, partiallycut away, of an individual high frequency radiating element 18. Thisdescription is also applicable to a low frequency element 20, since thetwo elements have similar structures, the essential difference being intheir relative sizes. The radiating element 18 is encased in a metalliccylindrical cartridge 44, preferably of Mu-metal, which serves as amagnetic shield and as a support structure for the components of theradiating element. The diameter of the radiating element isapproximately 0.2 wavelengths of the freespace radiation which istransmitted by this radiating element. This diameter is substantiallysmaller than the diameter of approximately one-half wavelengthcustomarily employed for cylindrical elements in phased array antennas.Because of this reduced diameter and the corresponding reduction in sizeof the radiating apertures of the individual radiating elements 18 and20 of the present invention, the front ends of these elements areequipped, as shown in FIG. 3, with a dielectrically loaded cylindricalwaveguide 52 and matching structure 46 which provide effective radiationfrom these smaller radiating apertures.

At the front end of the radiating element 18 the matching structure 46has the form of a cylindrical tubular segment or annulus of a ceramicmaterial, such as for example alumina, to provide for radiation from asmall aperture, in a well-known manner, by generating higher orderwaveguide modes. This type of matching structure is particularly adaptedto receive radiation over a range of scan angles which is characteristicof phased array antenna operation. Electromagnetic radiation propagateswithin the ceramic material of the matching structure 46 at a slowerspeed than in air. Due to the slower speed of propagation, therelatively small dimensions of the ceramic matching structure 46 aresufficiently large to support a number of waveguide modes which includethe dominant mode and higher order modes. The guide wavelengths of thesemodes depend on the scan angle, polarization and frequency of theradiation transmitted by the antenna array 12. In order to supportapproximately five propagating modes which transmit most of the radiatedpower, the matching structure 46 is typically constructed so that thedifference between its inner and outer radius is equal approximately totwo wavelengths of the radiation transmitted in a medium of this type ofceramic material; and the axial length of the matching structure 46 istypically four wavelengths of the radiation which is transmitted in amedium of this type of ceramic material. The matching structure 46 isreciprocal so that multiple modes are generated both with incident andtransmitted radiation. The combination of the dominant plus the higherorder modes of radiation provide for a radiation efficiency andbandwidth from a small aperture, such as the present radiating aperturehaving a diameter of approximately 0.2 wavelengths of the free spaceradiation, which approximates that of a radiator transmitting in thedominant mode from an aperture having a diameter of approximately 0.5wavelengths of the free-space radiation. Upon receiving radiation, thematching structure 46 provides the aforementioned modes, and with theaid of the dielectrically loaded cylindrical waveguide 52 and awellknown impedance transformer 54 which give differential phasevelocities to these waveguide modes, the plurality of these waveguidemodes are combined to produce a single circular waveguide mode, the TEmode at the junction of transformer 54 and phase shifter 56. This modeis desirable since it facilitates operation of the phase shifter 56. Thecircular waveguide 52 also compensate for the mutual coupling betweenthe individual radiating elements which transmit radiation of the samefrequency, so that each of these radiating elements can impart thedesired phase shift to the radiation essentially independently of thephase shift being imparted by the other elements.

The section of circular waveguide 52 is adjacent the matching structure46 and is dielectrically loaded with materials having differentdielectric constants in order to impart the aforementioned differentialphase velocities to the various waveguide modes. While several differentdielectric materials can be used, it has been found by experimentationthat the use of two dielectric materials, quartz and ceramic forexample, is sufficient to provide the differential phase velocities. Accordingly, a quartz rod 58 is disposed along the axis of the waveguide52 and is mounted within a ceramic l060l l 0139 cylinder 60, thedimensions of which will be described. The ceramic cylinder 60 issupported by the metallic case 44 which also serves as the waveguidewall. The use of the two different dielectrics results in a nonlinearityin the differences between the phase velocities of the various waveguidemodes whereby the several wavefronts of each of these modes from thematching structure 46 advance along the waveguide 52 to reach theterminus of the waveguide 52 with a small difference in their respectivephases. The difference in the phases of their respective wavefronts isfurther reduced in the impedance transformer 54 so that a singlewavefront, that of the TE mode, is launched into the phase shifter 56.In order to combine the wavefronts of approximately five waveguidemodes, the difference between the outer and inner radii of the ceramicdielectric cylinder 60 is typically one wavelength of the radiationtransmitted in a medium of this ceramic material; the radius of thequartz dielectric rod 58 is typically two wavelengths of the radiationtransmitted in a medium of this quartz material; and the axial length ofthe circular waveguide 52 is typically eight wavelengths of theradiation which is transmitted in a medium of this quartz material.

The impedance transformer 54 which is positioned between thedielectrically loaded waveguide 52 and the phase shifter 56 is in theform of an annulus of dielectric material, preferably of ceramic,supported within a metallic support 62. In combination, the ceramicannulus of the impedance transformer 54 and the metallic support 62 actas a short section of circular waveguide which launches the TE mode intothe phase shifter 56. In order to combine the wavefronts ofapproximately five waveguide modes, the difference between the outer andinner radii of the ceramic annulus of the impedance transformer 54 istypically four wavelengths of the radiation which is transmitted in amedium of this ceramic material; and the axial length of the impedancetransformer is typically one and one-half wavelengths of the radiation,which is transmitted in a medium of this ceramic material.

The compensation for the mutual coupling between radiating elementstransmitting at like frequencies of radiation is effected by virtue ofthe fact that the combination of matching structure, dielectricallyloaded waveguide, and impedance transformer matches the higher orderwaveguide modes induced by radiation incident upon the antenna arrayover the usual range of scanning angles typical of phased arrayoperation. Accordingly, waveguide modes induced by radiation fromadjacent elements are essentially not propagated through thedielectrically loaded waveguide and impedance transformer to the phaseshifter. The construction of the radiating element shown herein providesa relatively broad bandwidth in excess of approximately 8 percent.

In the embodiment of FIG. 1, each of the radiating elements 18 and 20provides the dual function of reflecting and imparting a phase shift tothe incident radiation. Accordingly, the radiating element 18, as shownin FIG. 3, contains phase shifter 56 terminated by a short-circuit inthe form of a metallic cap or disk 64 which reflects the radiation. Thephase shifter 56 has essentially the same form as that disclosed in thepatents to Francis J. OHara and Howard Scharfman,

US. Pat. No. 3,058,049 which issued Oct. 9, 1962 and U.S. Pat. No.3,100,287, which issued Aug. 6, I963. The phase shifter 56 comprises awaveguide structure having a dielectric cylinder 66 enclosing an innercore in the form of a ferrite rod 68, a metallic conducting cylindricalwall 70 typically formed by depositing silver on the outer surface ofthe dielectric cylinder 66, and a control coil 72, coaxially mountedwith the ferrite rod 68 and enclosing the cylindrical wall 70, whichcontrols the magnetic state of the ferrite rod 68. This type of phaseshifter responds to a circularly polarized wave of one sense only, andthereby minimizes cross-coupling between radiating elements whichrespond to circular polarization of the opposite sense. The control coil72 is connected via a pair of leads 74 to a coil driver circuit, notshown, of a standard well-known form, which is energized through pins 76in the back end of the radiating element 18 in a well-known manner toprovide the amount of phase shift required for a desired beam scanning.The cylindrical wall 70 of the phase shifter 56 is supported at itsfront end by a portion of the metallic support 62 and at its back end byan axial extension 78 of the short-circuit cap or disk 64.

In operation therefore, computer generated signals, not shown, areapplied to the pins of the radiating elements to energize the coildriver circuit, not shown. In each radiating element the coil drivercircuit supplies current to the controlcoil to provide the magneticfield in the ferrite rod which, in turn imparts a phase shift betweenthe incident and reflected radiation. The high frequency elements andthe low frequency elements of FIG. 1 receive separate sets of computergenerated drive signals so that high and low frequency beams ofradiation can be directed independently of each other. The matchingstructure, the dielectrically loaded cylindrical waveguide, and theimpedance transformer function in combination as a unit which provides abroadband impedance match from the radiating aperture at the matchingstructure to the phase shifter, and also compensates for mutual couplingamong adjacent radiating elements.

Referring now to FIGS. 4 and 5, there are shown two alternativeembodiments of the present invention in which the radiating elements 18and 20 are interleaved in alternative configurations. Theseconfigurations provide a spacing between centers of the higher frequencyradiating elements 18 which is less than or approximately equal toone-half the free space wavelength of the radiation transmitted byelement 18, and a spacing between centers of the lower frequencyradiating elements 20 which is less than or equal to one-half the freespace wavelength of the radiation transmitted by element 20. Thediameter of each radiating element in FIGS. 4 and 5 is approximately 0.2wavelengths of the free space radiation transmitted by that radiatingele ment. In both figures there is shown a perspective view of a portionof an interleaved antenna array wherein the radiating elements 18 and 20are affixed to a mounting plate by bolts 30 in contact with the mountingflanges 36 and 42, said mounting plate being designated by 80 in FIG. 4and by 82 in FIG. 5.

In the embodiment of FIG. 4, the smaller size higher frequency radiatingelements 18 are located at the in tersections of a grid of equilateraltriangles, not shown, the same grid, hereinafter designated thereference I060l l 0140 grid, that has been described earlier in thedescription of FIGS. 1 and 2. Each of the larger size, lower frequencyradiating elements is located at the intersections of another gridhaving the same cell form and size as that of the reference grid anddisplaced from the reference grid so that each lower frequency element20 is located at a center of a cell of the reference grid. Thus, thespacing between centers of the larger elements 20 is equal to thespacing between centers of the smaller elements 18, giving a spacingratio of 1:1 Thus, in the situation where the higher frequency is equalto twice the lower frequency, the configuration provides for a range ofbeam scanning angles for the lower frequency radiation which issubstantially larger than that for the higher frequency, as is sometimesrequired in radar search applications.

In FIG. 5, the smaller size, higher frequency radiating elements 18 arelocated at the intersections of the reference grid of equilateraltriangles in the same manner as shown in FIGS. 1, 2, and 4. The largersize, lower frequency radiating elements 20 are located at theintersections of a grid having equilateral triangular cells which arelarger than those of the reference grid by a factor of the square rootof3 and being offset from the reference grid, whereby every individualhigh frequency element 18 is abutting one, and only one, of thelarger-size, lower frequency elements 20, thereby providing a spacingratio of V721. This spacing ratio also provides a larger scan anglecapability at the lower frequency but not as large as that provided bythe configuration of FIG. 4.

Referring now to FIGS. 6 and 7, there is shown a perspective view of aportion of an interleaved antenna array which by way of example, shows atypical means for mounting the radiating elements in an alternativeembodiment of the present invention, wherein the larger size, lowerfrequency radiating elements 84 are mounted coaxially with and behind analternative form 86 of the smaller size, higher frequency radiatingelements 18. The higher frequency radiating element 86, as modified,does not contain the coil driver circuit and the electrical connectingpins 76 of radiating element 18, so that a simpler electrical connectioncan be made via a pair of coil leads 88A and 88B connecting directly tothe phase shifter coil, not shown in FIGS. 6 and 7, of element 86. Thecoil driver circuit, not shown, for radiating element 86 can be mountedbeneath the lower frequency radiating element 84. The smaller size,higher frequency elements 18 and 86 are located at the intersections ofthe reference grid, not shown. The larger elements 84 are located alongthe reference grid lines at every second intersection, thereby providinga spacing ratio 2;l.

The diameters of all the radiating elements are approximately 0.3wavelengths of the radiation which is transmitted by the radiatingelements. The spacing between centers of the higher frequency elements86 and I8 is approximately one-half the free space wavelength of theradiation transmitted by these elements, and similarly, the spacingbetween centers of the lower frequency elements 84 is approximatelyonehalf the free space wavelength of the radiation transmitted by thelower frequency elements 84. Each of the higher frequency coaxiallymounted elements 86 is supported by four plastic struts 90, of amounting bracket inserted in the oversized apertures of mounting plate94. Each of the lower frequency coaxially mounted elements 84 issupported by a metallic cylinder 92. The struts are made from materialwhich is essentially transparent to the radiation, and are used tosupport the high frequency elements 86 in coaxial relation with thelower frequency elements 84. The struts 90 are affixed to the metallicmounting plate 94, as shown in the sectional view of FIG. 7, by mountingbolts 96 and strut flange 98. The higher frequency radiating element 86is connected to the struts 90 by means of bolts 30, and nuts 100 whichare bonded to the underside of the struts 90. The metallic cylinder 92,as shown in FIG. 6, is affixed to the mounting plate 94 by mountingbolts 102 inserted through the upper cylinder mounting flange 104 andserves to direct the radiation from the lower frequency element 84outwards through the opening 106 in the mounting plate 94. The lowerfrequency element 84 is affixed by bolts, not shown, to the lowercylinder flange 108 of the metallic cylinder 92. The two wire leads 88Aand 88B extend through small holes in the metallic cartridge of element86 and also through two holes, not shown, in metallic cylinder 92. Theleads are parallel and lie in a plane containing the axis of theradiating element 86, with a spacing between them of )t /4 where A, isthe guide wavelength of the radiation transmitted by the lower frequencyelement 84. The spacing of .,/4 has been selected to minimizereflections in the transmission of the lower frequency radiation throughthe metallic cylinder 92.

It is understood that the above-described embodiments of the inventionare illustrative only, and modifications thereof will occur to thoseskilled in the art. For example, three or more different types ofradiating elements differing in polarization and in frequency can beinterleaved in a phased array antenna; other phased array antennaconfigurations with spacing ratios such as 2, 3 and 4 can be utilized;other forms of matching structures for the radiating elements such as aceramic annulus mounted at the front end of the radiating element withinthe waveguide segment can be utilized; other forms of electromagneticradiating elements such as dipoles having a loading structure foreffective radiation can be interleaved in such electronically beamsteered phased array antennas; three or more radiating elements can bemounted coaxially in the interleaved array and the antenna type of feedcan be of other forms such as the cassegrain, and a lens type of phasedarray antenna in which the feed horns are located behind the interleavedantenna array can be used. Accordingly, it is desired that thisinvention is not to be limited to the embodiments disclosed herein butis to be limited only as defined by the appended claims.

We claim:

1. A phased array antenna including groups of electromagnetic radiatingelements in which the radiating elements of one group having a radiationcharacteristic which is of a lower frequency and is circularly polarizedare interleaved with the radiating elements of a second group having aradiation characteristic which is of a higher frequency and iscircularly polarized in the opposite sense to the polarization of theradiation characteristic of the first group, at least one of saidradiating elements of said first group having a radiating aperturehaving dimensions less than one-third wavelength of the radiation whichis characteristic for that radiating element, at least one of saidradiating elements of said first group having a matching structure toprovide a radiation characteristic for said radiating element which issubstantially equal to the radiation characteristic provided for asimilar radiating element having an aperture with dimensions of one-halfwavelength, the radiating elements in each of said groups being solocated within the phased array antenna that the distance betweencenters of the radiating elements in any one group is substantiallyone-half wavelength of the radiation which is characteristic to thatgroup.

2. The system of claim 1 in which the radiating elements in at least oneof each of said groups have a cylindrical form.

3. The system of claim 1 in which a plurality of the radiating elementsdrawn from a plurality of said groups are coaxially mounted with respectto each other.

4. A phased array antenna in which a first group of radiating elementswhich form a first beam of electromagnetic radiation at a firstfrequency are interleaved with a second group of radiating elementswhich form a second beam of electromagnetic radiation at a secondfrequency substantially equal to one-half the first frequency,individual elements of said first group of elements being located at aplurality of the intersections of a first grid formed by three sets ofparallel lines which intersect to form grid cells each of which have theform of equilateral triangles a side of which is substantially equal toa half wavelength of said first radiation, the elements of said secondgroup of elements being located at a plurality of the intersections of asecond grid formed by three sets of parallel lines which intersect toform grid cells each of which have the form of equilateral triangles, aside of a grid cell of said second grid being parallel to and having alength equal to twice the length of a side of a grid cell of said firstgrid, an intersection of said second grid being located at the center ofa grid cell of said first grid, whereby the range of scan angles of saidfirst beam of radiation is substantially equal to the range of scanangles of said second beam of radiation.

5. The system of claim 4 in which individual radiating elements of saidgroups have radiating apertures whose dimensions are substantially lessthan one-third wavelength of the free space radiation transmitted andreceived by such radiating elements. each of such radiating elementshaving a dielectrically loaded matching structure which provides aradiation characteristic which is substantially the same as theradiation characteristic provided by an aperture of dimensionssubstantially one-half wavelength of said free space radiation.

6. An antenna array comprising a plurality of groups of electromagneticradiating elements in which the radiating elements of one group of saidgroups imparting a first phase characteristic to radiation transmittedfrom said one group are interleaved with radiating elements ofa secondgroup of said groups of radiating elements, said radiating elements ofsaid second group imparting a second phase characteristic to radiationtransmitted from said second group, said second phase characteristicbeing variable with respect to said first phase characteristic, saidradiating elements of said one group comprising a first cylindricaldielectric member and a second dielectric member coaxial to said firstmember for transmitting circularly polarized radiation, at least one ofsaid radiating elements of said one group having a radiating aperturewhose dimensions are less than approximately one-third wavelength of theradiation which is characteristic for that radiating element.

7. A phased array antenna comprising: a first set of electromagneticradiating elements arranged for forming a first beam of radiation, theelements of said first set being so located within the phased arrayantenna that the distance between centers of these radiating elements isapproximately one-half wavelength of radiation radiated by theseelements;

a second set of electromagnetic radiating elements arranged for forminga second beam of radiation, the radiating elements of said second setbeing so located within the phased array antenna that the distancebetween centers of the radiating elements of said second set isapproximately one-half wavelength of the radiation emitted by saidelements of said second set, a radiating element of said second set ofradiating elements being interleaved among the radiating elements ofsaid first set of radiating elements such that a radiating element ofsaid second set of radiating elements is positioned between radiatingelements of said first set of radiating elements, the radiating elementsof said second set being of physically smaller size than the radiatingelements of said first set to permit said interleaving of said elementof said second set among said elements of said first set; and

means for varying the phase independently of the frequency of radiationemitted by a radiating ele ment of said first set of radiating elementswith respect to the phase of radiation emitted by another radiatingelement of said first set of radiating elements to permit a variation inthe orientation of said first beam of radiation relative to anorientation of said second beam of radiation.

8. A phased array antenna comprising:

a first set of electromagnetic radiating elements arranged for forming afirst beam of radiation;

a second set of electromagnetic radiating elements arranged for forminga second beam of radiation, a radiating element of said second set ofradiating elements being interleaved among the radiating elements ofsaid first set of radiating elements such that a radiating element ofsaid second set of radiating elements is positioned between radiatingelements of said first set of radiating elements;

means for varying the phase independently of the frequency of radiationemitted by a radiating element of said first set of radiating elementswith respect to the phase of radiation emitted by another radiatingelement of said first set of radiating elements to permit a variation inthe orientation of said first beam of radiation relative to anorientation of said second beam of radiation; and

a plurality of the radiating elements of said first set comprising afirst cylindrical dielectric member, a second dielectric member coaxialto said first dielectric member for coupling to circularly polarizedradiation, and reflector means responsive to a preselected sense ofcircularly polarized l060l l 0142 radiation for reflecting radiantenergy through said first and said second dielectric members.

9. An antenna array comprising:

a plurality of groups of electromagnetic radiating elements;

the elements of a first group of said plurality of groups of radiatingelements being arranged for forming a first electronically steerablebeam of radiation;

the elements of a second group of said plurality of groups of radiatingelements being arranged for forming a second electronically steerablebeam of radiation, the radiating elements in said second groupcomprising means for making them insensitive to radiation having thefrequency and the polarization of the radiation of the elements of saidfirst group;

means for positioning individual elements of said second group ofradiating elements among elements of said first group of radiatingelements for interleaving said second group of radiating elements withsaid first group of radiating elements;

the distance between centers of the radiating elements in any one groupof said groups of radiating elements being approximately one halfwavelength of the radiation which is characteristic to that group;

means for varying the phase independently of the frequency of radiationof one of said elements of said first group of radiating elements withrespect to another element of said first group of radiating elements;and

means for varying the phase of radiation of one element of said secondgroup of radiating elements with respect to another element of saidsecond group of radiating elements independently of the phases of saidfirst group of radiating elements for independently steering a pluralityof beams of radiation relative to said antenna array.

10. An antenna array comprising:

a plurality of groups of electromagnetic radiating elements;

at first group of said plurality of groups of radiating elements beingarranged for forming a first electronically steerable beam of radiation;

a second group of said plurality of groups of radiating elements beingarranged for forming a second electronically steerable beam ofradiation;

means for positioning individual elements of said second group ofradiating elements among elements of said first group of radiatingelements for interleaving said second group of radiating elements withsaid first group of radiating elements;

means for varying the phase independently of the frequency of radiationof one of said elements of said first group of radiating elements withrespect to another element of said first group of said radiatingelements;

means for varying the phase of radiation of one element of said secondgroup of radiating elements with respect to another element of saidsecond group of radiating elements independently of the phases of saidfirst group of radiating elements for independently steering a pluralityof beams of radiation relative to said antenna array;

the distance between centers of the radiating elements in any one groupof said groups of radiating elements being approximately one-halfwavelength of the radiation which is characteristic to that group; and

the radiating elements in at least one group of said groups ofelectromagnetic radiating elements having radiating apertures havingdimensions which are less than approximately onethird wavelength of theradiation which is characteristic for such radiating elements, and inwhich the dimensions of the radiating apertures of said antenna arrayequal approximately the dimensions of the radiating aperture formed byan antenna array of the radiating elements of at least one of the groupsof said groups of electromagnetic radiating elements.

11. A phased array antenna comprising:

a first array of electromagnetic radiating elements emitting radiationhaving characteristics of a first frequency and a first polarization;

a second array of electromagnetic radiating elements emitting radiationhaving the characteristics of a second frequency and a secondpolarization;

means for positioning the radiating elements of said second array ofelectromagnetic radiating elements within cells of a grid composed oflines interconnecting the radiating elements of said first array ofelectromagnetic radiating elements;

at least one of the characteristics of frequency and polarization of theradiation of said first array being different from the characteristicsof frequency and polarization of the radiation of said second array;

the distance between centers of the radiating elements in any one arrayof said arrays of radiating elements being approximately one-halfwavelength of the radiation which is characteristic to that array;

means for varying the frequency of radiation of said first arrayindependently of the frequency of radiation of said second array; and

means for varying the phase independently of the frequency of radiationemitted by one element of said first array of electromagnetic radiatingelements relative to another element of said first array to permitsteering ofa beam of the radiation of said first array relative to abeam of the radiation of said second array.

12. The system as defined by claim 11 including means for steering abeam of radiation formed by the radiating elements of said first arrayindependently of a beam of radiation formed by the radiating elements ofsaid second array.

13. The system as defined by claim 12 in which the radiating elements ofsaid first array are spaced with reference to the radiating elements ofsaid second array in a configuration which provides a range of scanangles of said beam of radiation formed by radiating elements of saidfirst array which is substantially the same as the range of scan anglesof the beam of radiation formed by the radiating elements of said secondarray.

14. The system as defined by claim 12 in which the radiating elements ofsaid first array are spaced with reference to the radiating elements ofsaid second array to provide a range of scan angles in the radiationpattern of the radiating elements of said first array which issubstantially the same as the range of scan angles in the radiationpattern of radiating elements of said second array.

15. A phased array antenna comprising:

a first array of electromagnetic radiating elements emitting radiationhaving characteristics of a first frequency and a first polarization;

a second array of electromagnetic radiating elements emitting radiationhaving the characteristics of a second frequency and a secondpolarization, the elements of said second array comprising means formaking these elements insensitive to radiation having the frequency andpolarization of the radiation of elements of said first array;

means for interleaving the radiating elements of said second array ofelectromagnetic radiating elements among the radiating elements of saidfirst array of electromagnetic radiating elements; the distance betweencenters of the radiating elements in any one array of said arrays ofradiating elements being approximately one-half wavelength of theradiation which is characteristic to that array;

at least one of the characteristics of frequency and polarization of theradiation of said first array being different from the characteristicsof frequency and polarization of the radiation of said second array; and

means for varying the phase of radiation emitted by one element of saidfirst array of electromagnetic radiating elements relative to anotherelement of said first array to steer a beam of the radiation of saidfirst array independently of the orientation of a beam of the radiationof said second array.

16. The phased array antenna as defined by claim 15 wherein said firstarray radiating elements have a radiation characteristic of a firstfrequency, and said second array radiating elements have a radiationcharacteristic of a second frequency.

17. The phased array antenna as defined by claim 15 wherein theradiation polarization characteristic for said first array radiatingelements is polarized radiation in a first direction and the radiationpolarization characteristic for said second array radiating elements ispolarized radiation in a second direction.

18. The system as defined by claim 17 wherein the radiationcharacteristic of said first array radiating elements is at a firstfrequency and the radiation characteristic of said second arrayradiating elements is at a second frequency.

19. A phased array antenna comprising:

a first array of electromagnetic radiating elements emitting radiationhaving characteristics of a first frequency and a first polarization;

a second array of electromagnetic radiating elements emitting radiationhaving the characteristics of a second frequency in a secondpolarization;

means for interleaving the radiating elements of said second array ofelectromagnetic radiating elements among the radiating elements of saidfirst array of electromagnetic radiating elements;

at least one of the characteristics of frequency and polarization of theradiation of said first array being different from the characteristicsof frequency and polarization of the radiation of said second y meansfor varying the phase of radiation emitted by one element of this firstarray of electromagnetic radiating elements relative to another elementof said first array to steer a beam of the radiation of said first arrayindependently of the orientation of a beam of the radiation of saidsecond array; and

at least one of said first array radiating elements having a radiatingaperture having dimensions less than approximately one-third wavelengthof the radiation which is characteristic for that radiating element andhaving a matching structure to provide a radiation characteristic forthat radiating element which is approximately equivalent to theradiation characteristic for a radiating element without said matchingstructure and having a radiating aperture whose dimensions areapproximately one-half wavelength.

1. A phased array antenna including groups of electromagnetic radiating elements in which the radiating elements of one group having a radiation characteristic which is of a lower frequency and is circularly polarized are interleaved with the radiating elements of a second group having a radiation characteristic which is of a higher frequency and is circularly polarized in the opposite sense to the polarization of the radiation characteristic of the first group, at least one of said radiating elements of said first group having a radiating aperture having dimensions less than one-third wavelength of the radiation which is characteristic for that radiating element, at least one of said radiating elements of said first group having a matching structure to provide a radiation characteristic for said radiating element which is substantially equal to the radiation characteristic provided for a similar radiating element having an aperture with dimensions of one-half wavelength, the radiating elements in each of said groups being so located within the phased array antenna that the dIstance between centers of the radiating elements in any one group is substantially one-half wavelength of the radiation which is characteristic to that group.
 2. The system of claim 1 in which the radiating elements in at least one of each of said groups have a cylindrical form.
 3. The system of claim 1 in which a plurality of the radiating elements drawn from a plurality of said groups are coaxially mounted with respect to each other.
 4. A phased array antenna in which a first group of radiating elements which form a first beam of electromagnetic radiation at a first frequency are interleaved with a second group of radiating elements which form a second beam of electromagnetic radiation at a second frequency substantially equal to one-half the first frequency, individual elements of said first group of elements being located at a plurality of the intersections of a first grid formed by three sets of parallel lines which intersect to form grid cells each of which have the form of equilateral triangles a side of which is substantially equal to a half wavelength of said first radiation, the elements of said second group of elements being located at a plurality of the intersections of a second grid formed by three sets of parallel lines which intersect to form grid cells each of which have the form of equilateral triangles, a side of a grid cell of said second grid being parallel to and having a length equal to twice the length of a side of a grid cell of said first grid, an intersection of said second grid being located at the center of a grid cell of said first grid, whereby the range of scan angles of said first beam of radiation is substantially equal to the range of scan angles of said second beam of radiation.
 5. The system of claim 4 in which individual radiating elements of said groups have radiating apertures whose dimensions are substantially less than one-third wavelength of the free space radiation transmitted and received by such radiating elements, each of such radiating elements having a dielectrically loaded matching structure which provides a radiation characteristic which is substantially the same as the radiation characteristic provided by an aperture of dimensions substantially one-half wavelength of said free space radiation.
 6. An antenna array comprising a plurality of groups of electromagnetic radiating elements in which the radiating elements of one group of said groups imparting a first phase characteristic to radiation transmitted from said one group are interleaved with radiating elements of a second group of said groups of radiating elements, said radiating elements of said second group imparting a second phase characteristic to radiation transmitted from said second group, said second phase characteristic being variable with respect to said first phase characteristic, said radiating elements of said one group comprising a first cylindrical dielectric member and a second dielectric member coaxial to said first member for transmitting circularly polarized radiation, at least one of said radiating elements of said one group having a radiating aperture whose dimensions are less than approximately one-third wavelength of the radiation which is characteristic for that radiating element.
 7. A phased array antenna comprising: a first set of electromagnetic radiating elements arranged for forming a first beam of radiation, the elements of said first set being so located within the phased array antenna that the distance between centers of these radiating elements is approximately one-half wavelength of radiation radiated by these elements; a second set of electromagnetic radiating elements arranged for forming a second beam of radiation, the radiating elements of said second set being so located within the phased array antenna that the distance between centers of the radiating elements of said second set is approximately one-half wavelength of the radiation emitted by said elements of said second set, a radiating element of said second set oF radiating elements being interleaved among the radiating elements of said first set of radiating elements such that a radiating element of said second set of radiating elements is positioned between radiating elements of said first set of radiating elements, the radiating elements of said second set being of physically smaller size than the radiating elements of said first set to permit said interleaving of said element of said second set among said elements of said first set; and means for varying the phase independently of the frequency of radiation emitted by a radiating element of said first set of radiating elements with respect to the phase of radiation emitted by another radiating element of said first set of radiating elements to permit a variation in the orientation of said first beam of radiation relative to an orientation of said second beam of radiation.
 8. A phased array antenna comprising: a first set of electromagnetic radiating elements arranged for forming a first beam of radiation; a second set of electromagnetic radiating elements arranged for forming a second beam of radiation, a radiating element of said second set of radiating elements being interleaved among the radiating elements of said first set of radiating elements such that a radiating element of said second set of radiating elements is positioned between radiating elements of said first set of radiating elements; means for varying the phase independently of the frequency of radiation emitted by a radiating element of said first set of radiating elements with respect to the phase of radiation emitted by another radiating element of said first set of radiating elements to permit a variation in the orientation of said first beam of radiation relative to an orientation of said second beam of radiation; and a plurality of the radiating elements of said first set comprising a first cylindrical dielectric member, a second dielectric member coaxial to said first dielectric member for coupling to circularly polarized radiation, and reflector means responsive to a preselected sense of circularly polarized radiation for reflecting radiant energy through said first and said second dielectric members.
 9. An antenna array comprising: a plurality of groups of electromagnetic radiating elements; the elements of a first group of said plurality of groups of radiating elements being arranged for forming a first electronically steerable beam of radiation; the elements of a second group of said plurality of groups of radiating elements being arranged for forming a second electronically steerable beam of radiation, the radiating elements in said second group comprising means for making them insensitive to radiation having the frequency and the polarization of the radiation of the elements of said first group; means for positioning individual elements of said second group of radiating elements among elements of said first group of radiating elements for interleaving said second group of radiating elements with said first group of radiating elements; the distance between centers of the radiating elements in any one group of said groups of radiating elements being approximately one-half wavelength of the radiation which is characteristic to that group; means for varying the phase independently of the frequency of radiation of one of said elements of said first group of radiating elements with respect to another element of said first group of radiating elements; and means for varying the phase of radiation of one element of said second group of radiating elements with respect to another element of said second group of radiating elements independently of the phases of said first group of radiating elements for independently steering a plurality of beams of radiation relative to said antenna array.
 10. An antenna array comprising: a plurality of groups of electromagnetic radiating elements; a first group of said plurality of groups of radiating elements being arraNged for forming a first electronically steerable beam of radiation; a second group of said plurality of groups of radiating elements being arranged for forming a second electronically steerable beam of radiation; means for positioning individual elements of said second group of radiating elements among elements of said first group of radiating elements for interleaving said second group of radiating elements with said first group of radiating elements; means for varying the phase independently of the frequency of radiation of one of said elements of said first group of radiating elements with respect to another element of said first group of said radiating elements; means for varying the phase of radiation of one element of said second group of radiating elements with respect to another element of said second group of radiating elements independently of the phases of said first group of radiating elements for independently steering a plurality of beams of radiation relative to said antenna array; the distance between centers of the radiating elements in any one group of said groups of radiating elements being approximately one-half wavelength of the radiation which is characteristic to that group; and the radiating elements in at least one group of said groups of electromagnetic radiating elements having radiating apertures having dimensions which are less than approximately one-third wavelength of the radiation which is characteristic for such radiating elements, and in which the dimensions of the radiating apertures of said antenna array equal approximately the dimensions of the radiating aperture formed by an antenna array of the radiating elements of at least one of the groups of said groups of electromagnetic radiating elements.
 11. A phased array antenna comprising: a first array of electromagnetic radiating elements emitting radiation having characteristics of a first frequency and a first polarization; a second array of electromagnetic radiating elements emitting radiation having the characteristics of a second frequency and a second polarization; means for positioning the radiating elements of said second array of electromagnetic radiating elements within cells of a grid composed of lines interconnecting the radiating elements of said first array of electromagnetic radiating elements; at least one of the characteristics of frequency and polarization of the radiation of said first array being different from the characteristics of frequency and polarization of the radiation of said second array; the distance between centers of the radiating elements in any one array of said arrays of radiating elements being approximately one-half wavelength of the radiation which is characteristic to that array; means for varying the frequency of radiation of said first array independently of the frequency of radiation of said second array; and means for varying the phase independently of the frequency of radiation emitted by one element of said first array of electromagnetic radiating elements relative to another element of said first array to permit steering of a beam of the radiation of said first array relative to a beam of the radiation of said second array.
 12. The system as defined by claim 11 including means for steering a beam of radiation formed by the radiating elements of said first array independently of a beam of radiation formed by the radiating elements of said second array.
 13. The system as defined by claim 12 in which the radiating elements of said first array are spaced with reference to the radiating elements of said second array in a configuration which provides a range of scan angles of said beam of radiation formed by radiating elements of said first array which is substantially the same as the range of scan angles of the beam of radiation formed by the radiating elements of said second array.
 14. The system as defined by claim 12 in which the radiating elements of said first array are spaced with reference to the radiating elements of said second array to provide a range of scan angles in the radiation pattern of the radiating elements of said first array which is substantially the same as the range of scan angles in the radiation pattern of radiating elements of said second array.
 15. A phased array antenna comprising: a first array of electromagnetic radiating elements emitting radiation having characteristics of a first frequency and a first polarization; a second array of electromagnetic radiating elements emitting radiation having the characteristics of a second frequency and a second polarization, the elements of said second array comprising means for making these elements insensitive to radiation having the frequency and polarization of the radiation of elements of said first array; means for interleaving the radiating elements of said second array of electromagnetic radiating elements among the radiating elements of said first array of electromagnetic radiating elements; the distance between centers of the radiating elements in any one array of said arrays of radiating elements being approximately one-half wavelength of the radiation which is characteristic to that array; at least one of the characteristics of frequency and polarization of the radiation of said first array being different from the characteristics of frequency and polarization of the radiation of said second array; and means for varying the phase of radiation emitted by one element of said first array of electromagnetic radiating elements relative to another element of said first array to steer a beam of the radiation of said first array independently of the orientation of a beam of the radiation of said second array.
 16. The phased array antenna as defined by claim 15 wherein said first array radiating elements have a radiation characteristic of a first frequency, and said second array radiating elements have a radiation characteristic of a second frequency.
 17. The phased array antenna as defined by claim 15 wherein the radiation polarization characteristic for said first array radiating elements is polarized radiation in a first direction and the radiation polarization characteristic for said second array radiating elements is polarized radiation in a second direction.
 18. The system as defined by claim 17 wherein the radiation characteristic of said first array radiating elements is at a first frequency and the radiation characteristic of said second array radiating elements is at a second frequency.
 19. A phased array antenna comprising: a first array of electromagnetic radiating elements emitting radiation having characteristics of a first frequency and a first polarization; a second array of electromagnetic radiating elements emitting radiation having the characteristics of a second frequency in a second polarization; means for interleaving the radiating elements of said second array of electromagnetic radiating elements among the radiating elements of said first array of electromagnetic radiating elements; at least one of the characteristics of frequency and polarization of the radiation of said first array being different from the characteristics of frequency and polarization of the radiation of said second array; means for varying the phase of radiation emitted by one element of this first array of electromagnetic radiating elements relative to another element of said first array to steer a beam of the radiation of said first array independently of the orientation of a beam of the radiation of said second array; and at least one of said first array radiating elements having a radiating aperture having dimensions less than approximately one-third wavelength of the radiation which is characteristic for that radiating element and having a matching structure to provide a radiation characteristic for that radiating element which is approximately equivalent to the radiation characteristic for a radiating element without said matching structure and having a radiating aperture whose dimensions are approximately one-half wavelength. 